1. Field of Invention
This invention is directed to one method and one apparatus to obtain broadband operation of a ferrite stripline edge-mode/standing-mode circulator/isolator. More specifically, this invention teaches to use a varying magnetic bias to broaden the transmission band of a ferrite stripline edge-mode/standing-mode circulator/isolator with improved characteristics.
2. Prior Art
Although ferrite stripline junction circulators have been described in the literature since the 1950's, their operation was only vaguely understood until the theoretical work by Bosma in 1964 (H. Bosma, “On stripline Y-circulation at UHF,” IEEE Microwave Theory Tech., vol. MTT-12, pp. 61-73, January 1964), and by Fay and Comstock in 1965 (C. E. Fay and R. L. Comstock, “Operation of the ferrite junction circulator,” IEEE Trans. Microwave Theory Tech., vol. MTT-13, pp. 15-27, January 1965). The operation of an edge-mode ferrite isolator was described by Hines in 1961 (M. E. Hines, “Reciprocal and Nonreciprocal Modes of Propagation in Ferrite Stripline and Microstrip Devices”, IEEE Trans. vol. MTT-19, pp. 442-451, 1961), and an edge-mode ferrite circulator by How in 2005 (H. How, “Magnetic Microwave Devices,” in Encyclopedia of RF and Microwave Engineering, Vol. 3, pp. 2425-2461, 2005). Since then, the prior art has always assumed that a ferrite circulator or isolator is operational under a magnetic bias field established via the use of permanent magnets whose explicit spatial profile is considered immaterial to the circuit performance, at least deemed not critical. The resultant frequency bandwidth is thus restricted to a 2:1 ratio (Y. S. Wu and F. J. Rosenbaum, “Wide-band operation of microstrip circulators,” IEEE Trans. Microwave Theory Tech., vol. MTT-22, pp. 849-856, October 1974), or a 3:1 ratio (M. G. Mathew and T. J. Weisz, “Microwave Transmission Devices Comprising Gyromagnetic Material Having Smoothly Varying Saturation Magnetization,” U.S. Pat. No. 4,390,853, Jun. 28, 1983).
There has been rapid development in RF and microwave technologies during the past decade. RF and microwave wireless applications have been and continue to be among the fastest growth areas. Some of the expanding activities in these fields include wireless communications (mobile, cellular, and satellite), wireless sensors, local area networks, remote control and identification, global positioning systems (GPS), and intelligent highway and vehicle systems (IHVS). Circulators and isolators are indispensable building elements in RF and microwave circuits: they are used whenever isolation is intended among circuit modules, separating the signal paths according to their propagation directions thereby allowing the transmitter and the receiver to multiplex. Also, broadband instrumentations are needed by the electronic testing industries so that universal equipments are possible whose operation is independent of frequency. As the market is always hungry for bandwidths, the need for broadband circulators and isolators with improved transmission characteristics is thus clear and evident.
3. Objects and Advantages
Accordingly, it is an object of the invention to address one or more of the foregoing disadvantages or drawbacks of the prior art, and to provide such an improved method and apparatus to obtain improved broadband circulator/isolator operation by properly shaping the bias magnetic field. The bias magnetic field is thus shaped not only to satisfy the necessary circulation conditions for the circulator or isolator circuit, but also to partially magnetize the ferrite material thereby forming a gradual transition to warrant broadband operation; the radial component is reduced and discontinuity in magnetization is minimized, resulting in improved characteristics of the circulator or isolator performance.
Other objects will be apparent to one of ordinary skill, in light of the following disclosure, including the claims.